Many scholars have theorized that economic development, particularly industrialization and urbanization, contributes to the growth of participatory democracy; according to this theory, it would seem logical that women would both demand and gain suffrage in ever greater numbers whenever economic development expanded their economic opportunities. However, the economic development theory is inadequate to explain certain historical facts about the implementation of women's suffrage. For example, why was women's suffrage, instituted nationally in the United States in 1920, not instituted nationally in Switzerland until the 1970s? Industrialization was well advanced in both countries by 1920: over 33 percent of American workers were employed in various industries, as compared to 44 percent of Swiss workers. Granted, Switzerland and the United States diverged in the degree to which the expansion of industry coincided with the degree of urbanization: only 29 percent of the Swiss population lived in cities of 10,000 or more inhabitants by 1920. However, urbanization cannot fully explain women's suffrage. Within the United States prior to 1920, for example, only less urbanized states had granted women suffrage. Similarly, less urbanized countries such as Cambodia and Ghana had voting rights for women long before Switzerland did. It is true that Switzerland's urbanized cantons (political subdivisions) generally enacted women's suffrage legislation earlier than did rural cantons. However, these cantons often shared other characteristics—similar linguistic backgrounds and strong leftist parties—that may help to explain this phenomenon.